QRasterPixmapData: Reuse underlying QImage in fill() if possible.

When switching from a format without alpha channel to one that has it,
reuse the underlying QImage memory if the old & new color depths match.

This avoids one allocation when using the rather common pattern:

    QPixmap pixmap(w, h);
    pixmap.fill(Qt::transparent);

Reviewed-by: Samuel Rødal

1 files changed, 36 insertions, 0 deletions

diff --git a/src/gui/image/qimage_p.h b/src/gui/image/qimage_p.h
index c687448..e054814 100644
--- a/src/gui/image/qimage_p.h
+++ b/src/gui/image/qimage_p.h
@@ -112,6 +112,42 @@ struct Q_GUI_EXPORT QImageData {        // internal image data
 
 void qInitImageConversions();
 
+inline int qt_depthForFormat(QImage::Format format)
+{
+    int depth = 0;
+    switch(format) {
+    case QImage::Format_Invalid:
+    case QImage::NImageFormats:
+        Q_ASSERT(false);
+    case QImage::Format_Mono:
+    case QImage::Format_MonoLSB:
+        depth = 1;
+        break;
+    case QImage::Format_Indexed8:
+        depth = 8;
+        break;
+    case QImage::Format_RGB32:
+    case QImage::Format_ARGB32:
+    case QImage::Format_ARGB32_Premultiplied:
+        depth = 32;
+        break;
+    case QImage::Format_RGB555:
+    case QImage::Format_RGB16:
+    case QImage::Format_RGB444:
+    case QImage::Format_ARGB4444_Premultiplied:
+        depth = 16;
+        break;
+    case QImage::Format_RGB666:
+    case QImage::Format_ARGB6666_Premultiplied:
+    case QImage::Format_ARGB8565_Premultiplied:
+    case QImage::Format_ARGB8555_Premultiplied:
+    case QImage::Format_RGB888:
+        depth = 24;
+        break;
+    }
+    return depth;
+}
+
 QT_END_NAMESPACE
 
 #endif